System for identification of a tag on a moving item

ABSTRACT

Provided is a system for identification of an item, wherein the system includes a conveyor belt, a positioning device and a reader operable to receive at least one reading, wherein the positioning-device is configured to retrieve a first position of the item) at a first time instant before the first antenna and a second position of the item at a second time instant after the first antenna, the first and second time instants defining a time window, wherein the reader is configured to extract from each reading retrieved by the first antenna a measurement of the phase of the signal transmitted by the tag and perform a data processing of the phase measurements, whereby the identification of the item is accomplished.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. applicationSer. No. 15/542,780 filed on Jul. 11, 2017, which claims priority to PCTApplication No. PCT/DK2015/050008 having a filing date of Jan. 14, 2015,the entire contents both of which is hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to the technical field of item identification,particularly to identification of moving items.

BACKGROUND

Item identification may be performed, for example, in case of trackingand routing a passenger bag within airport premises, by installing readpoints through which the conveyor belt transporting that bag run.Conventional read points typically use the received signal strengthindicator (RSSI) to determine which bag tag is attached to the bag.However, the latter is a very unreliable type of measurement, whichdepends on numerous factors such as the propagation environment, thequality of the tag and the antenna, the consistency in the quality ofthe tag, etc. As a consequence, the probability of misidentification ishigh. In order to alleviate this problem, shielding panels and RFabsorbing panels may be installed by the read point to ensure thatreadings only from the bag tag on the item moving past the antenna arereceived. However, this implies a higher infrastructure cost.

Hence, there is a long-felt need in the technical field of itemidentification of overcoming the abovementioned drawbacks of thestate-of-the-art solutions.

SUMMARY

An aspect relates to an improvement to the state-of-the-art. The secondaspect of the invention is to solve the aforementioned drawbacks of theknown art by providing a highly accurate and reliable itemidentification system without increasing the cost of the infrastructure.

The aspects of the embodiments of the invention are achieved by a systemfor identification of an item (e.g., a suitcase, a bag, a package,etc.), wherein the system comprises a conveyor belt, a positioning meansor positioning device (e.g., a conveyor belt controller such as a PLC ora pair of photoelectric sensors) and a reader (e.g., an RF reader suchas an RFID reader) operable to receive at least one reading at at leastone first antenna from at least one tag (e.g., a self-adhesive labelembedding an RFID tag) attached to the item (e.g., at the handle of asuitcase), the first antenna (e.g., an RFID antenna) being adapted to bearranged at a read point along the conveyor belt (e.g., underneath thetopside and/or at one or both lateral sides of an opening of a wall, agate, a portal, etc. through which the conveyor belt runs), wherein thepositioning means or device is configured to retrieve a first positionof the item at a first time instant before the first antenna and asecond position of the item at a second time instant after the firstantenna, the first and second time instants defining a (configurable)time window, wherein the reader is configured to extract (e.g., by meansof signal processing techniques) from each reading retrieved by thefirst antenna a measurement of the phase (e.g., an estimate of the phasechange over time) of the signal (e.g., an RF signal) transmitted by thetag and perform a data processing of the phase measurements, which dataprocessing comprises constructing a phase curve from the phasemeasurements and determining a global maximum on the phase curve,wherein the reader is configured to associate the tag to the item if theglobal maximum lies within the time window, whereby the identificationof the item (i.e., the association of the tag to the item andconsequently to the travel information of the passenger) isaccomplished.

Herein, “RFID” is referred to any technology that uses RF signals forcommunication and/or identification purposes such as UHFGen2.

A reading may, for example, comprise: the time when the signal has beenreceived at the reader (i.e., the timestamp), the RSSI, the phase valueof the received signal and information about the communication channel.As well as the RSSI, the derivative of the phase value providesinformation on the change in distance between the antenna and the item.

The embodiments of the invention have the following advantages: (i) itis independent of the signal strength; (ii) it does not result in anymisidentification error; and (iii) it is very precise and reliable.Also, there is no need to continuously track the items (e.g., by theconveyor belt controller), but just to install antennas in strategicpoints along the way, e.g., where the item shall be moved from oneconveyor belt to another conveyor belt or where the item shall be x-rayscanned so that the result of the scanning can be associated to the itemin a database or where the item shall be routed towards a specificdestination (e.g., a flight).

Theoretically, the power of the reader could be even increased up to itsmaximum in order to get as many measurements for the same item aspossible (e.g., 3-4 m before/after the first antenna) while notinfluencing the retrieved phase values. If RSS measurements would beused, instead, the higher the power of the reader the more difficultwould be to filter the data and perform the identification. Hence, theembodiments of the invention have the additional advantage of enabling amore accurate item identification while being able to increase radioemissions for better signal reception.

Advantageously, the first antenna of the reader may be placed with anequal distance from the first position of the item at the first timeinstant and the second position of the item at the second time instant,so as to maximize the probability of reading the tag both when the tagis approaching the read point and when the tag is moving away from theread point after having moved past it. Moreover, the first antenna maybe arranged so as to be as close as possible to the items moving pastit, whereby the readings retrieved by the first antenna have the highestreceived signal strength possible. Therefore, RSSI may be used incombination with embodiments of the invention in order to filter thephase measurements, for example, by discarding phase measurements with areceived signal strength under a threshold (e.g., −55 dBm).

A phase reconstruction generates a non-periodic curve from the phasemeasurements, which have a periodicity of 360 degrees (actually,depending on the reader used, they may also be represented with aperiodicity of 180 degrees). The global maximum in the curverepresenting the reconstructed phase (referred to as the phase curve)denotes the time when the tag is approximately by the first antenna ofthe reader.

Due to the physics and the position of the first antenna, the latter hasa coverage of, for example, a few meters (e.g., before and after itsnadir), and therefore may retrieve data from a number of tags (e.g.,tags from items before/after the item to identify), not only from thedesired one. Thus, there might be many phase measurements falling withinthe time window not belonging to the tag attached to the item to beidentified. Nevertheless, the system is able to discard all the tagsthat do not belong to the item in question by constructing the phasecurve and determining that the global maximum does not fall within thetime window.

Hence, this data processing is beneficial, for example, in case of manyreadings from many different tags within the time window, so as to moreeasily be able to identify the pattern of each tag and filter out theirrelevant tags.

In an advantageous embodiment of the invention, the reader is configuredto construct the phase curve by detecting period roll overs of the phasemeasurements (e.g., when the phase value shifts from the maximum of theperiod, such as 180 or 360 degrees, to the minimum of the period, suchas 0 degrees, or vice versa) and adding period fragments.

In an advantageous embodiment of the invention, the reader is furtherconfigured to compare the speed related to consecutive constructed phasemeasurements (calculated from the phase and time values) to the speed ofthe conveyor belt (e.g., 2 m/s) and accordingly filter out constructedphase measurements lying too far from each other.

In an advantageous embodiment of the invention, the reader is furtherconfigured to verify the global maximum by defining an interval alongthe constructed phase curve around the global maximum (e.g., 2 secbefore and after the global maximum), calculating a decline (i.e., aphase difference) before and after the global maximum, and comparing thecalculated declines to a threshold (e.g., depending on the speed of theconveyor belt and the height of the first antenna). For example, thethreshold may be within the range of 100-500 degrees for a conveyor beltthat runs at 2 msec.

Note that, in case the phase measurements of a tag do not change butremain constant during the time window, the system can infer that thetag is not moving and is not attached to the item (e.g., if it hasfallen on the floor by the side of the conveyor belt). The system wouldthen be able to filter out those tags not matching the movement patternof the item. Hence, embodiments of the invention has the furtheradvantage of enabling the detection of such situations and, optionally,of subsequently alerting the user (e.g., a passenger) or an operator(e.g., an airport clerk).

In an advantageous embodiment of the invention, the reader furthercomprises at least one second antenna (e.g., an RFID antenna) adapted tobe placed underneath an upper surface of the conveyor belt, wherein thereader is configured to associate the tag to the item if at least onereading (e.g., 80% of the readings) has been retrieved from the secondantenna for the tag within the time window. Note that, in case thesecond antenna is placed by the same read point along the conveyor beltwhere the first antenna is placed, the time window is the same for bothantennas. Otherwise, each antenna may have its own time windowrepresenting the time interval spanning from a time instant before theantenna to a time instant after the antenna.

Advantageously, another unit in the system (e.g., a local server) ratherthan the reader may perform the extraction of the phase measurementsfrom the readings and/or the association of the tag to the item and/orthe comparison of the phase measurements to the threshold and/or thedata processing.

Also, the aforementioned aspects of the embodiments of the invention areachieved by a method of identification of an item, wherein the methodcomprises:

-   -   providing a system as described above;    -   the reader receiving one or more readings from the tag;    -   the positioning means retrieving the position of the item at the        first time instant before the first antenna and at the second        time instant after the first antenna, the first and second time        instants defining a time window;    -   the reader extracting from each reading retrieved by the first        antenna a measurement of the phase of the signal transmitted by        the tag;    -   the reader performing a data processing of the phase        measurements, which data processing comprises constructing a        phase curve from the phase measurements and determining a global        maximum on the phase curve; and    -   the reader associating the tag to the item if the global maximum        lies within the time window; whereby the identification of the        item is accomplished.        In an advantageous embodiment of the invention, the method        further comprises constructing the phase curve by detecting        period roll overs of the phase measurements and adding period        fragments.

In an advantageous embodiment of the invention, the method furthercomprises comparing the speed related to consecutive constructed phasemeasurements to the speed of the conveyor belt and accordingly filteringout constructed phase measurements lying too far from each other.

In an advantageous embodiment of the invention, the method furthercomprises verifying the global maximum by defining an interval along theconstructed phase curve around the global maximum, calculating a declinebefore and after the global maximum, and comparing the calculateddeclines to a threshold.

In an advantageous embodiment of the invention, the method furthercomprises:

-   -   providing a system as described above;    -   the reader associating the tag to the item if at least one        reading has been retrieved from the second antenna for the tag        within the time window.

Note that the steps of the method do not necessarily need to be carriedout in the order described above but may also be performed in adifferent order and/or simultaneously.

Note that all the aforementioned advantages of the system are also metby the method described above.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with reference tothe following figures, wherein like designations denote like members,wherein:

FIG. 1: depicts a top view of a Conveyor belt reader;

FIG. 2: depicts a snapshot of phase measurements plotted against timefor the first antenna;

FIG. 3: depicts a snapshot of two reconstructed phase curves; and

FIG. 4: is a method of item identification according to embodiments ofthe invention.

NOTATIONS

-   1: Conveyor belt reader.-   2: Item.-   3: Conveyor belt.-   3′: Upper surface of the conveyor belt.-   4: Read point.-   4′: Topside of the read point.-   5: Tag.-   6: Measurement.-   7: Phase curve.-   8: Global maximum.-   9: First antenna.-   10: Coverage of the first antenna.-   t₁: First time instant.-   t₂: Second time instant.-   W: Time window.

DETAILED DESCRIPTION

FIG. 1 shows an advantageous embodiment of a system 1 for identificationof an item 2 in the form of a conveyor belt reader 1 in an airport.Note, however, that the system 1 of the invention is not limited to beused as a conveyor belt reader 1 within airport premises, but can alsobe used for other applications such as in a postal distribution centralor a retail distribution center for sorting packages.

A suitcase 2 is transported on a conveyor belt 3, which runs through aread point 4 in the direction of the arrow. The conveyor belt 3 has anRFID antenna (the second antenna) of an RFID reader placed underneathits upper surface 3′ (not shown in FIG. 1) and the read point 4 has anRFID antenna 9 (the first antenna 9) of the RFID reader placedunderneath its topside 4′. The first antenna 9 retrieves readings withinits coverage 10, in particular from an RFID tag attached to the suitcase2 (not shown in FIG. 1).

The printer at the check-in codes the relevant information in the RFIDtag, which is printed together and embedded in the bag tag 5 to apply tothe suitcase 2. The 10 digits code, which is encoded in the barcode onthe bag tag 5, is also encoded in the RFID tag via the RFID antenna atthe printer.

A PLC (Programmable Logic Controller) is a low level controller, whichmakes the conveyor belt 3 run/stop and which tracks the bags 5 by meansof photocells positioned along the conveyor belt 3.

The conveyor belt controller knows the first time instant t₁ when thesuitcase 2 is at a first check-point before the read point 4 (e.g., itmay be where a first photocell of the PLC is placed or where the PLCexpected the suitcase 2 to be at that time instant) and the second timeinstant t₂ when the suitcase 2 is at a second check-point after the readpoint 4 (e.g., it may be where a second photocell of the PLC is placedor where the PLC expected the suitcase 2 to be at that time instant).For example, the first and second check-points may be around 1 m beforeand after the read point 4 (i.e., before and after both the first andsecond antennas). When the suitcase 2 has run through the read point 4,the conveyor belt controller may inform the reader that at the firsttime instant t₁ the suitcase 2 was at the first check-point and at thesecond time instant t₂ the suitcase 2 was at the second check-point.

The exemplary identification method 100 (ref. FIG. 4) carried out inthis embodiment mainly comprises two steps. First, it is checked whetherthere is at least one reading from the second antenna falling within thetime window W, which is defined by the time interval between t₁ and t₂.If so, it is concluded that the bag tag 5 sat on that suitcase 2. Notethat, especially in case of items 2 where the bag tag 5 hangs on theside or gets underneath the underside of the item 2 when the latter isplaced on the conveyor belt 3, it may be difficult to retrieve data fromthe first antenna 9. If not (e.g., the bag tag 5 sat on the top of theitem 2 and the second antenna could not receive signal from it or thereare no readings during the time interval in which the second antenna isswitched on), a phase curve 7 is constructed from the phase measurements6 retrieved by the first antenna 9 and the global maximum 8 of the phasecurve 7 is determined. The global maximum 8 represents the time instantwhen the bag tag 5 has essentially passed underneath the first antenna9. The reader then associates that bag tag 5 to the suitcase 2 if theglobal maximum 8 lies within the time window W. After the identificationhas been performed, the information concerning which bag tag 5 sits onthat suitcase 2 is passed back to the conveyor belt controller, whichcontinues to track and route the suitcase 2 onwards.

FIG. 2 shows measured phase values 6 in degrees against time in ms forthe bag tags 5 under coverage of the second antenna. The latter may havea confined coverage such that it may retrieve signals only when thesuitcase 2 travels in proximity of its zenith (the solid lineapproximately in the middle of the time window W). Consequently, thereader may not receive signals from other items 2 lying before, after oron the side of the second antenna (e.g., 40 cm from it), thus there maybe no need to construct the phase curve 7 as with the phase measurements6 retrieved by the first antenna 9, but only to check whether thetimestamps of the reading fall within the time window W; if so, the bagtag 5 is associated to the suitcase 2.

The second antenna may be displaced with respect to the nadir of thefirst antenna 9 (e.g., slightly before it), as the second antenna has tobe inserted underneath the upper surface 3′ of the conveyor belt 3,basically where there is space to place it. Hence, the readings got fromthe second antenna may be offset with respect to the middle of the timewindow W. Nevertheless, the offset is known by the reader, which cantherefore subtract it from the timestamps of the readings.

FIG. 3 shows measured phase values 6 in degrees against time in ms forthe bag tags 5 under coverage of both the first antenna 9 and the secondantenna. With respect to the second antenna, which in this embodimenthas a confined coverage, the first antenna 10 has a broader coverage andtherefore retrieves many more readings, for example, due to other items2 lying before, after or on the side of the first antenna 9. As it isnoticeable from the phase curve 7, the phase measurements 6 have aperiodicity between 0 and 180 degrees, and the constructed phase curve 7increases/decreases the closer/farther the suitcase 2 is with respect tothe first antenna 9, reaching its peak (i.e., the global maximum 8)approximately when the suitcase 2 is at the nadir of the first antenna9.

Note that there may be periods with no readings if the first antenna 9and the second antenna switch between each other and do not transmitsimultaneously. For example, the first antenna 9 may transmit for around150 ms and then the second antenna for around 50 ms. In other cases, itmay be possible that the suitcase 2 is stopped until it can be movedfrom a first conveyor belt to a second conveyor belt, where it is, e.g.,accelerated into an empty wagon for transporting it forward through theread point 4, thus a plateau for the phase values 6 can be observedright before the global maximum 8.

FIG. 4 shows a method 100 of identification of an item 2, wherein themethod 100 comprises:

-   -   providing 101 a system 1 as described above;    -   the reader receiving 102 one or more readings from the tag 5;    -   the reader extracting 103 from each reading retrieved by the        first antenna 9 a measurement 6 of the phase of the signal        transmitted by the tag 5;    -   the conveyor belt controller retrieving 104 the position of the        item 2 at the first time instant t₁ before the first and second        antennas and at the second time instant t₂ after the first and        second antennas, the first and second time instants t₁, t₂        defining a time window W;    -   the reader associating 105 the tag 5 to the item 2 if at least        one reading 6 has been retrieved from the second antenna for the        tag 5 within the time window W; otherwise, the reader performing        106 a data processing of the phase measurements 6, which data        processing comprises constructing 107 the phase curve 7 from the        phase measurements 6 and determining 108 the global maximum 8 on        the phase curve 7, and the reader associating 109 the tag 5 to        the item 2 if the global maximum 8 lies within the time window        W;        whereby the identification of the item 2 is accomplished.

Although the present invention has been disclosed in the form ofpreferred embodiments and variations thereon, it will be understood thatnumerous additional modifications and variations could be made theretowithout departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of “a” or“an” throughout this application does not exclude a plurality, and“comprising” does not exclude other steps or elements. The mention of a“unit” or a “module” does not preclude the use of more than one unit ormodule.

1. A system for identification of an item, wherein the system comprises:a conveyor belt, a reader comprising a first antenna, the first antennabeing arranged at a read point along the conveyor belt and configuredfor receiving a signal transmitted from a tag, the reader being operableto receive at least one reading from the tag via the first antenna;wherein the reader is configured to extract from each reading retrievedby the first antenna a measurement of the phase of the signaltransmitted by the tag; a conveyor belt controller configured toretrieve a first position of the item at a first time instant before thefirst antenna and a second position of the item at a second time instantafter the first antenna, the first and second time instants defining atime window, wherein the reader or a local server in the system isconfigured for performing a data processing of the phase measurements,which data processing comprises constructing a phase curve from thephase measurements, the phase curve expressing the signal phase independence of time, and determining a global maximum on the phase curve,wherein the reader is configured for associating the tag to the item ifthe global maximum lies within the time window.
 2. The system accordingto claim 1, wherein the reader further comprises at least one secondantenna placed underneath an upper surface of the conveyor belt, thesecond antenna being displaced from the read point; wherein the systemis configured for determining a time offset, the time offsetcorresponding to the time it takes for the conveyor belt to convey anitem on the conveyor belt from the first antenna to the second antennaand for determining a further time window that is offset by the timeoffset; wherein the reader is configured for associating the tag to theitem if at least one reading has been retrieved from the second antennafor the tag within the further time window.
 3. The system according toclaim 1, wherein the tag is an RFID tag, and the first antenna is anRFID antenna.
 4. The system according to claim 1, wherein the at leastone reading comprises a timestamp for receipt of the signal from thetag, a signal strength indicator, RSSI, for the signal, the signal phasevalue of the signal, and information about a communication channel forthe signal.
 5. The system according to claim 4, wherein the reader isconfigured for providing a signal strength threshold and for discardingphase measurements when a received signal has a strength under thesignal strength threshold.
 6. The system according to claim 1, whereinthe item is a suitcase, or a bag, or a package in an airport.
 7. Thesystem according to claim 1, wherein the reader is configured toconstruct the phase curve by detecting period roll overs of the phasemeasurements and adding period fragments.
 8. The system according toclaim 1, wherein the reader is further configured to compare the speedrelated to consecutive constructed phase measurements to the speed ofthe conveyor belt and accordingly filter out constructed phasemeasurements matching the movement pattern of the item.
 9. The systemaccording to claim 1, wherein the reader is further configured to verifythe global maximum by defining an interval along the constructed phasecurve around the global maximum, calculating a decline before and afterthe global maximum, and comparing the calculated declines to athreshold.
 10. The system according to claim 1, wherein the readerfurther comprises at least one second antenna adapted to be placedunderneath an upper surface of the conveyor belt, wherein the reader isconfigured to associate the tag to the item if at least one reading hasbeen retrieved from the second antenna for the tag within the timewindow.